<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      canvas {
        background-color: rgba(255, 0, 0, 0.1);
      }
    </style>
  </head>
  <body>
    <canvas id="tutorial" width="300px" height="300px">
      浏览器不兼容canvas
    </canvas>
    <script>
      window.onload = function () {
        //1.拿到canvas的元素对象
        let canvasE1 = document.getElementById("tutorial");

        if (!canvasE1.getContext("2d")) {
          return;
        }
        // 2.拿到canvas渲染的上下文
        let ctx = canvasE1.getContext("2d");
      };

      // 在浏览器下一次重绘之前会回调函数的回调函数drow
      requestAnimationFrame(draw);
      function draw() {
        console.log("deaw");
        requestAnimationFrame(draw);
      }
    </script>
  </body>
</html>
